Femtocell configuration using spectrum sensing

ABSTRACT

An embodiment of the present invention provides for the ad-hoc configuration of femtocells using spectrum sensing for the selection of spectrum channels. One or more embodiments of the invention determine frequency bands that are not reserved by macrocells in a location, and perform spectrum sensing to determine communication channels in unreserved frequency bands that are being used by other femtocells in range. In this manner, femtocells can be deployed and configured in an ad-hoc manner without external coordination or control between deployed femtocells.

FIELD OF THE INVENTION

An embodiment of the present invention generally relates to wirelesstelecommunications and more particularly to the detection and analysisof wireless spectrum.

BACKGROUND

Global System for Mobile Communications (GSM) telecommunication systemsprovide wireless communication to mobile devices over a radio accessnetwork (RAN) operating in licensed bandwidth. A RAN typically consistsof several macrocells, otherwise known as base transceiver stations(BTS). Each macrocell of a network is typically connected to a basestation controller (BSC). The BSC controls and monitors variousactivities of the macrocells. For example, the BSC may help tocoordinate handoff of a mobile device moving from one macrocell coveragearea to another. The BSC may also coordinate operating bandwidth withneighboring macrocells to avoid interference. As the bandwidth used bymobile applications continues to increase, there is a demand to increasenetwork capacity through frequency reuse.

Femtocells, picocells, and microcells, hereinafter referred tocollectively as femtocells, are small, low-power base stations designedto provide better coverage for small residential structures, high-demandpublic locations or other hard to cover areas. Femtocells operate in alicensed spectrum with the authorization of the licensee and use abroadband data connection to send data to and receive data from thelicensee network. Femtocells have a limited range of coverage, and assuch, multiple femtocells may operate within a macrocell area.

Femtocells provide several advantages. For end-users, femtocells mayreduce wireless data charges, improve indoor coverage, and reduce powerconsumption of mobile devices. For network operators, femtocells improvecoverage, improve capacity by reducing the amount of macrocell bandwidthused, reduce traffic between a provider's macrocell and wired networks,and reduce the operator's maintenance and infrastructure costs.

Femtocells typically operate in one of two configurations. The femtocellmay act as an extension to the existing network of macrocells networkand provide coverage for all network users or the femtocell access maybe limited to a particular set of users.

The placement and bandwidth spectrum utilized by a femtocell mayadversely interfere with the operation of macrocells or otherneighboring femtocells. In 3GPP Long Term Evolution (LTE) systems,connections are established in unique orthogonal frequency domainmultiplexed (OFDM) subcarrier channels. LTE macrocells generally use thesame frequency bands. Macrocells coordinate with each other to givemobile users at the edge of a macrocell coverage area a different subsetof the available OFDM subcarriers to avoid interference. Likemacrocells, femtocells must operate in using a set of OFDM subcarriersthat are unique from its neighboring femtocells in order to avoidinterference. Because femtocells operate outside of a coordinatednetwork, similar coordination is generally not possible. One or moreembodiments of the present invention may address one or more of theseissues.

SUMMARY

In one embodiment of the present invention, a method is provided fordetermining available wireless communication channels. Unreservedfrequency bands in a location are determined. A first channel within oneof the determined unreserved frequency bands is selected and signalsreceived on the first channel are monitored for a time duration. A powerspectral density of the signals during the time duration is estimated. Aspectral moving average of the estimated power spectral density isdetermined. A detection threshold for the first channel is determinedalong with a percentage of a bandwidth of the spectral moving average ofthe estimated power spectral density that exceeds the detectionthreshold. In response to the determined percentage being less than aselected percentage, data is stored indicating the first channel isavailable. In response to the determined percentage being greater thanor equal to the selected percentage, it is determined whether anormalization of the spectral moving average of the estimated powerspectral density is consistent with a selected signal shape. In responseto determining the estimated averaged power spectral density is notconsistent with the selected signal shape, data is stored indicating thefirst channel is available.

In another embodiment, a system is provided for determining availablewireless communication channels. The system includes a receiver unitconfigured to receive signals transmitted on a plurality ofcommunication channels and output signals received on a selectedchannel. An input storage unit is coupled to an output of the receiverunit and coupled to a data bus. The system also includes a signalprocessing unit, a processing unit, a memory unit, a storage unit, andan input-output control unit coupled to the data bus. The processingunit and signal processing unit are configured to: determine unreservedfrequency bands in a location, select the selected channel from one ofthe determined unreserved frequency bands, and configure the receiverunit to output signals received on the selected channel. The processingand signal processing units further determine a power spectral densityof the signals output by the receiver unit and determine from the powerspectral density whether the signals received on the selected channelare consistent with a selected signal shape and strength indicating thechannel is not available.

In yet another embodiment, a circuit for determining available wirelesscommunication channels is provided. The circuit includes a receivercircuit configured to receive a plurality of transmitted signals and asignal processing circuit coupled to an output of the receiver circuit.A channel analysis circuit is coupled to the signal processing circuitand a channel selection controller circuit is coupled to the channelanalysis circuit and to the receiver circuit. The channel selectioncontroller circuit monitors the plurality of transmitted signalsreceived by the receiver circuit, determines unreserved channels in alocation, selects a first channel from the determined unreservedchannels, and configures the receiver circuit to output signals receivedon the first channel. The signal processing circuit determines andoutputs a power spectral density of signals output by the receivercircuit. The channel analysis circuit determines a spectral movingaverage of the power spectral density output by the signal processingcircuit, determines a signal detection threshold level, and determinesthe percent of bandwidth of the first channel with a power spectraldensity above the signal detection threshold level. The channel analysiscircuit additionally normalizes the determined spectral moving average,determines a peak and a slope of the normalized spectral moving average,and determines from the percentage and the peak and the slope whetherthe first channel is available.

It will be appreciated that various other embodiments are set forth inthe Detailed Description and Claims which follow.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects and advantages of the invention will become apparentupon review of the following detailed description and upon reference tothe drawings in which:

FIG. 1 is a block diagram illustrating the geographical coverage of aGSM macrocell and LTE femtocell in a GSM communication network;

FIG. 2-1 shows a flowchart of a process for determining availablewireless channels for femtocell operation;

FIG. 2-2 illustrates an estimated power spectral density of a femtocellchannel;

FIG. 2-3 illustrates a spectral moving average of an estimated powerspectral density;

FIG. 2-4 illustrates a normalized spectral moving average of anestimated power spectral density;

FIG. 2-5 illustrates determined slopes of a normalized spectral movingaverage of an estimated power spectral density;

FIG. 3 shows a flowchart of a process for analyzing potentiallyavailable channels, and determining the channel with the least amount ofnoise present;

FIG. 4 shows a block diagram of a circuit for determining availablechannels in accordance with an embodiment of the invention.

FIG. 5 is a block diagram of an example programmable logic integratedcircuit which can be configured in accordance with an embodiment of theinvention;

FIG. 6 illustrates a block diagram of a computing arrangement systemconfigured to determine available wireless communication channels inaccordance with an embodiment of the invention;

FIG. 7 illustrates a block diagram of an example implementation ofsignal processing hardware configured to implement several signalprocessing functions.

DETAILED DESCRIPTION OF THE DRAWINGS

Many existing wireless communication standards, such as the UniversalMobile Telecommunications System (UMTS) or the IEEE 802.11b standard,operate under an interrupt-based system where users poll thecommunication medium to acquire communication slots. Under thesestandards, multiple base stations can operate using the same frequencyband. Interference between base stations is mitigated though codedivision multiple access (CDMA), wherein each base station operatesunder a unique scrambling code, orthogonal to other base stations. Othercommunication networks, such as the Global System for MobileCommunications (GSM), utilize frequency division multiple access (FDMA)to avoid interference and increase bandwidth utilization through thereuse of frequencies in distinct regions of operation.

Unlike UMTS, Long Term Evolution (LTE) requires exclusive frequencyaccess. LTE operates using orthogonal frequency-division multiple access(OFDMA) in the downlink and signal-carrier frequency-division multipleaccess (SC-FDMA) in the uplink. OFDMA is a multi-user version oforthogonal frequency-division multiplexing (OFDM), where a selectedbandwidth for the downlink communication channel is divided into a largenumber of closely spaced orthogonal sub-bands that are used to carrydata. SC-FDMA is a linearly precoded OFDMA scheme to have lowerpeak-to-average power ratio in the uplink transmissions. LTE supportsboth time-division duplexing (TDD), where downlink and uplinkcommunication channels share the same frequency band in a time-slottedfashion, and frequency-division duplexing (FDD), where uplink anddownlink communication channels are located in separate frequency bands.Based on the bandwidth efficiency it provides, TDD is considered to be apreferable option in LTE. Subcarriers in the uplink and downlinkcommunication channels of a LTE basestation are shared in time andfrequency by LTE users based on their uplink and downlink trafficdemands. To avoid interference, a LTE femtocell basestation mustcommunicate using uplink and downlink communication channels that arenot overlapping in frequency with those channels used by neighboringfemtocells within the range.

Because an unused portion of bandwidth is required, it is likely thatLTE systems will be deployed in vacant GSM spectrum made availablethrough frequency reuse. When LTE femtocells are deployed in bandwidthof a GSM macrocell network, the femtocells must operate usingcommunication channels selected from frequency bands distinct from thosebeing used by macrocells in range. Additionally, femtocells must operateusing communication channels that are distinct from those used byneighboring femtocells. One or more embodiments of the present inventionprovides for the ad-hoc configuration of femtocells using spectrumsensing for the selection of communication channels. One or moreembodiments of the invention determine frequency bands that are notreserved by macrocells in a location, and perform spectrum sensing todetermine communication channels, within the unreserved frequency bands,that are being used by other femtocells in range. In this manner,femtocells can be deployed and configured in an ad-hoc manner withoutexternal coordination or control between deployed femtocells.

In networks that utilize frequency reuse, the network covers a region,which is divided and covered by several macrocells. Frequencies can bereused for non-adjacent macrocells according to a frequency reusefactor, which depends on the reuse pattern used for deployment. Thefrequency reuse factor is 1/K where K is the number of frequency groupsused. Common frequency reuse factors are ⅓, ¼, 1/7, or 1/9. If the totallicensed bandwidth is B, the bandwidth available for use in eachmacrocell is B/K.

FIG. 1 is a block diagram illustrating the geographical coverage of acommunication network of GSM macrocells with LTE femtocells deployedwithin the coverage area of several macrocells. Grid 120 shows a blockof licensed frequencies that has been divided into nine frequency bands.In this illustration, macrocells, exemplified by hexagons 130, 132, and134, are evenly distributed so each covers approximately the same area.In this example, each hexagon represents the macrocell and the regioncovered by the macrocell. Between any two neighboring macrocell regions,some overlap exists where signals can be received by both macrocells. Toavoid interference at locations of macrocell overlap, distinct sets offrequency bands for communication are reserved for neighboringmacrocells. In this example layout, three distinct sets are required toavoid interference between macrocells. The nine frequency bands aredivided into three groups of frequency bands A, B, and C that are evenlydistributed over the licensed spectrum. The frequency distribution isgenerally decided and frequency bands are assigned to each macrocell bya base station controller (BSC) 140. BSC 140 communicates with themacrocells to assign frequency bands and transfer data between thenetwork and each macrocell using wired network resources 142, such asfiber optics. Note that BSC 140 communicates with all the macrocells ofFIG. 1, though the communication channel 142 is shown to connect BSC 140to only three of the macrocells.

Several LTE femtocells 104, 106, 108, and 110 may also operate, coveringsmaller sub-regions within the macrocells. To avoid interference withmacrocell operation, femtocells must avoid using bandwidth of frequencybands assigned to macrocells operating in the femtocell location. Forexample, femtocell 104 is located within macrocell region 130. Macrocell130 operates under frequency group A, which includes frequency bands 1,4, and 7 of licensed spectrum distribution 120. Therefore, femtocell 104must operate using bandwidth within a frequency band from groups B or C.

For clarity, frequency bands or spectrum assigned to macrocells presentin a location are referred to as reserved frequency bands. Frequencybands or spectrum not assigned to any macrocell in the location arereferred to as available frequency bands. Spectrum used by a femtocellfor wireless communication is referred to as a communication channel.Channels not used by other femtocells are referred to as availablechannels, and channels that are being used by other femtocells arereferred to as unavailable channels. It is understood that the bandwidthof spectrum used for a communication channel need not be the same as thefrequency bands allocated to macrocells or the same as the bandwidthused by individual mobile devices to communicate with macrocells. Forexample, the bandwidth of one frequency band may be sufficient tosupport multiple femtocell channels.

Femtocell 106 is located within a region covered by two macrocellsoperating under frequency band groups B and C. Therefore, femtocell 106must select a channel within a frequency band of group A.

Femtocells must also avoid using channels used by other femtocellswithin range. Two femtocells 108 and 110 are located within the regioncovered by macrocell 132, which operates in frequency band group B.Therefore, femtocells 108 and 110 must select distinct frequencychannels from frequency bands contained in groups A and C, which includefrequency bands 1, 3, 4, 6, 7, and 9.

One or more embodiments of the invention are applicable to severalcommunication standards including IEEE 802.16 (WiMAX), 3GPP-LTE, andother standards which require an exclusive set of frequency bands andwhere neighbor femtocells periodically send signals on each band in theexclusive set, even when no user communication is performed. Forexample, a standard may periodically communicate synchronization andcontrol signals. These signals may be time-slotted, but they have to betransmitted on the entire frequency band, as is the case for LTE. Theinvention is also understood to be applicable to various networks inwhich unreserved spectrum is available, as in FDMA deployment.

FIG. 2-1 shows a flowchart of a process for determining availablewireless channels for femtocell operation. Macrocells present in alocation of femtocell operation are detected and frequency bands thatare not reserved for those detected macrocells are determined at step202. In GSM networks, macrocells can be detected by monitoring thebroadcast control channel (BCCH) carrier in the GSM downlink todetermine the identity of the macrocell base station(s) in step 201.Once macrocell identifiers are obtained, the femtocell can look upfrequency bands reserved for the macrocell(s) from a database. Thedatabase may be created and maintained by the base station controller(BSC) and may be accessed using the broadband connection used by thefemtocell to connect to the licensee's network. One or more embodimentsof the invention may retrieve frequency bands reserved for themacrocells in the location using a user input location identifier, suchas a zip code. In such embodiments, macrocell identifiers need not beobtained.

An unreserved frequency band in the licensed spectrum is selected as apotential channel at step 204. The power spectral density of thepotential channel is estimated at step 206. FIG. 2-2 shows an exampleillustration of an estimated power spectral density of a channel. Thefrequency range of the power spectral density is equal to the bandwidthof the potential channel. A moving average of the estimated powerspectral density in the frequency domain is calculated at step 208. Oneor more embodiments refer to the moving average in the frequency domainas the spectral moving average and such terms are used interchangeablyherein.

The moving average in the frequency domain is calculated using a slidingfrequency domain window. The width of the window is set to the same sizeas the bandwidth of a femtocell signal without guard-bands. The centerpoint of the window is moved along the frequency band of the channel insteps. At each step, the moving average of the power spectral density atthe frequency of the center point is equal to the average of powerspectral density data points within the window. FIG. 2-3 illustrates thespectral moving average of the power spectral density of FIG. 2-2.Application of spectral moving average windowing has the effect ofsmoothing the estimated power spectral density and, because the width ofthe moving average window is selected to fit the bandwidth of theexpected LTE signal, the moving averaging effectively correlates thespectral footprint with an LTE signal shape. If the signal is an LTEsignal, the signal shape created is a triangle with a peak at the centerfrequency. The spectral moving average of the power spectral density isalso referred to as the spectral averaged power spectral density or thespectral average and such terms are used interchangeably herein

A detection threshold of signal strength corresponding to datatransmission is determined from the spectral averaged power spectraldensity at step 212. The detection threshold is determined from,

δ=μ+c*σ

where μ is the mean signal strength within the frequency band of thepotential channel, c is a positive constant, and σ is the standarddeviation. The standard deviation σ is used to ensure that signal spikesfrom background noise are not recognized at a transmitted data signal.Constant c acts as a scaler of the standard deviation and can be used toplace the threshold slightly above the mean value plus standarddeviation. Typical values for c are near the value 1. FIG. 2-3,illustrates the calculated detection threshold 230 superimposed on thespectral moving average. Frequency band 232 is the portion of thespectral average that is greater than the detection threshold.

The percentage of the spectral average with a level greater than thedetermined detection threshold is determined at step 214. If the signalis an LTE signal generated by another femtocell, it is expected that thebandwidth of the area above the threshold is around 50 to 70 percent ofthe total bandwidth of the channel. If the determined percentage is lessthan or equal to a predetermined percent of channel bandwidth atdecision step 226, data is stored indicating the channel is availablefor use by the femtocell at step 222.

If the determined percentage is less than or equal to a predeterminedpercent of channel bandwidth at decision step 226, the averaged powerspectral density is normalized at step 210. Normalization increases ordecreases the amplitude of the spectral averaged power spectral densityto a set amplitude value by uniformly scaling the amplitude over thechannel bandwidth. FIG. 2-4 illustrates the spectral averaged powerspectral density shown in FIG. 2-3 after normalization to a setamplitude 234. It will be appreciated that normalization may beperformed at any point after determining the spectral moving average ofthe estimated power spectral density at step 208 and beforedetermination of peak and slopes at step 228.

The normalized power spectral density is analyzed at steps 228 and 220to determine whether it is consistent with the expected shape of asignal transmitted by another femtocell. In this example implementation,the shape is determined from the slopes of the normalized power spectraldensity. If the signal is an LTE signal generated by another femtocell,the slopes of the normalized power spectral density are expected to fallwithin a range of slopes.

The peak and the slopes of the normalized power spectral density aredetermined at step 228 for the portion of the frequency band determinedto be greater than the detection threshold in step 214. FIG. 2-5illustrated determined slopes 236 superimposed on the normalized powerspectral density. If the determined slopes are not within the expectedrange, data is stored indicating the channel is available for use by thefemtocell at step 222. Conversely, if the determined slopes are withinthe expected range at decision step 220, data is stored at step 224indicating the channel is not available. If the channel is determined tobe not available at decision step 220, another channel is selected fromthe unreserved portion of the licensed bandwidth at step 204. Theprocess is repeated until an available channel is determined.

One or more embodiments of the present invention continue to analyzechannels after an available channel is found to determine the availablechannel with the least amount of noise present.

FIG. 3 shows a flowchart of a process for analyzing potentiallyavailable channels, and determining the channel with the least amount ofnoise present. Frequency bands reserved to macrocells present in alocation of femtocell operation are determined at step 302. A potentialcommunication channel is selected from the licensed frequency bands notreserved to macrocells in the location at step 304. The processdetermines whether the selected channel is available at step 306. Thisdetermination is performed in the manner shown in FIG. 2. Data is storedindicating whether the channel is available along with a noise level ofthe channel at step 308. The noise level may be determined in any numberof ways. One example process for determining the noise level is tocalculate the average amplitude of the power spectral density over thefrequency band of the channel. The process repeats until all potentialchannels have been analyzed.

When decision step 310 determines all potential channels have beenchecked, the available channel with the lowest level of noise present isdetermined at step 312. If no channel is determined to be availableafter analysis of all potential channels, one or more embodiments willselect the channel with the lowest level power spectral density tominimize interference with other femtocells. In such embodiments, dataindicating the signal level of unavailable channels is stored at step308 until an available channel is found. After an available channel isfound, only information for channels determined to be available needs tobe stored.

FIG. 4 is a block diagram of an example implementation of a circuitarrangement for determining available wireless communication channels inaccordance with one or more embodiments of the invention. The circuitarrangement includes a receiver circuit 410, a signal processing circuit420, a channel analysis circuit 430, and a channel selection controlcircuit 450. The receiver circuit is configured to receive a pluralityof transmitted signals and output signals received on a selected channelto the signal processing circuit 420. The selected channel is set bychannel selection control circuit 450. The channel selection controlcircuit 450 is configured to monitor signals received by receivercircuit 410, and determine channels, which are unreserved in thelocation in which the circuit arrangement is operating. The channelselection circuit sets the selected channel to one of the determinedunreserved channels.

After the selected channel has been set, the signals received on theselected channel are output by the receiver circuit to signal processingcircuit 420. The signal processing circuit 420 is configured tocalculate the power spectral density of the signals received from thereceiver circuit 410. In the example implementation, the signalprocessing circuit 420 includes a circuit 422 for calculating the FastFourier Transform of the signal received. The calculated Fast FourierTransform is output to and processed by circuit 424, which determinesthe square magnitude of the Fast Fourier Transform. The square magnitudeis output to and averaged over a time duration by circuit 426 todetermine the power spectral density.

The determined power spectral density is output to channel analysiscircuit 430. The channel analysis circuit 430 is configured to determinefrom the power spectral density whether the channel is available.Circuit 430 includes circuit 432 for determining the spectral movingaverage of the power spectral density in the frequency domain. Asdiscussed above, a channel is determined to be unavailable if a certainpercentage of the channel bandwidth is above a detection threshold levelor if the slope of the averaged and normalized power spectral density iswithin a certain range. Circuit 430 includes a threshold detectioncircuit 434 coupled to the output of circuit 432. The thresholddetection circuit 434 is configured to determine a detection thresholdand the percentage of channel bandwidth above the detection threshold.To determine peak and slopes of the power spectral density, channelanalysis circuit 430 includes normalizer circuit 436 that normalizes aportion of the averaged power spectral density output by circuit 432that is above the detection threshold determined by circuit 434.

One or more embodiment of the present invention alternately performnormalization prior to detecting a threshold. In such embodiments,normalizer circuit 436 is coupled to the output of circuit 432 andoutputs a normalized spectral moving average to threshold detectioncircuit 434.

The normalized power spectral density is output to peak and slopedetection circuit 438, which is configured to determine the peak andslopes of the normalized portion of the power spectral density. Waveformanalyzer 440 receives the determined percentage above threshold fromcircuit 434 and determined peak and slopes from circuit 438. If thedetermined percentage is below a selected value or if the determinedslopes are outside of a selected range, waveform analysis circuit 440outputs a signal to the channel selection control circuit 450 indicatingthat the selected channel is available.

In one or more embodiments of the invention, the output of channelanalysis circuit 430 is received by channel selection control circuit450, as shown. If channel analysis circuit 430 indicates the channel isunavailable, channel selection control circuit 450 selects a new channelfrom the determined unreserved channels and configures receiver circuit410 to receive and output transmitted signals on the new channel. Ifchannel analysis circuit 430 indicates the channel is available, channelselection control circuit stores data indicating the selected channel isavailable. In one or more embodiments of the invention that analyze allchannels, the channel selection control circuit stores data indicatingthe available channel with the lowest power spectral density.

It is understood that the various portions of the circuit may beimplemented using dedicated hardware, programmable logic, or withvarious processing architectures.

FIG. 5 is a block diagram of an example programmable logic integratedcircuit, which can be configured in accordance with one or moreembodiments of the invention. Programmable logic integrated circuitsinclude several different types of programmable logic blocks in thearray. For example, FIG. 5 illustrates an field programmable gate array(FPGA) architecture (500) that includes a large number of differentprogrammable tiles including multi-gigabit transceivers (MGTs 501),configurable logic blocks (CLBs 502), random access memory blocks (BRAMs503), input/output blocks (IOBs 504), configuration and clocking logic(CONFIG/CLOCKS 505), digital signal processing blocks (DSPs 506), areconfiguration port (RECONFIG 516), specialized input/output blocks(I/O 507), for example, clock ports, and other programmable logic 508such as digital clock managers, analog-to-digital converters, systemmonitoring logic, and so forth. Some FPGAs also include dedicatedprocessor blocks (PROC 510).

In some FPGAs, each programmable tile includes a programmableinterconnect element (INT 511) having standardized connections to andfrom a corresponding interconnect element in each adjacent tile.Therefore, the programmable interconnect elements taken togetherimplement the programmable interconnect structure for the illustratedFPGA. The programmable interconnect element INT 511 also includes theconnections to and from the programmable logic element within the sametile, as shown by the examples included at the top of FIG. 5.

For example, a CLB 502 can include a configurable logic element CLE 512that can be programmed to implement user logic plus a singleprogrammable interconnect element INT 511. A BRAM 503 can include a BRAMlogic element (BRL 513) in addition to one or more programmableinterconnect elements. Typically, the number of interconnect elementsincluded in a tile depends on the height of the tile. In the picturedembodiment, a BRAM tile has the same height as four CLBs, but othernumbers (e.g., five) can also be used.

A DSP tile 506 can include a DSP logic element (DSPL 514) in addition toan appropriate number of programmable interconnect elements. DSP tilesare dedicated hardware designed to perform specialized functions. Inaccordance with one or more embodiments of the invention, a DSP tile 506may be configured to perform one or signal processing functions such as,Fast Fourier Transform, square magnitude, average over time, spectralmoving average over a selected bandwidth, etc.

An IOB 504 can include, for example, two instances of an input/outputlogic element (IOL 515) in addition to one instance of the programmableinterconnect element INT 511. As will be clear to those of skill in theart, the actual I/O pads connected, for example, to the I/O logicelement 515 are manufactured using metal layered above the variousillustrated logic blocks, and typically are not confined to the area ofthe input/output logic element 515.

In the pictured embodiment, a columnar area near the center of the die(shown shaded in FIG. 5) is used for configuration, clock, and othercontrol logic. Horizontal areas 509 extending from this column are usedto distribute the clocks and configuration signals across the breadth ofthe FPGA.

Some FPGAs utilizing the architecture illustrated in FIG. 5 includeadditional logic blocks that disrupt the regular columnar structuremaking up a large part of the FPGA. The additional logic blocks can beprogrammable blocks and/or dedicated logic. For example, the processorblock PROC 510 shown in FIG. 5 spans several columns of CLBs and BRAMs.

Note that FIG. 5 is intended to illustrate only an exemplary FPGAarchitecture. The numbers of logic blocks in a column, the relativewidths of the columns, the number and order of columns, the types oflogic blocks included in the columns, the relative sizes of the logicblocks, and the interconnect/logic implementations included at the topof FIG. 5 are purely exemplary. For example, in an actual FPGA more thanone adjacent column of CLBs is typically included wherever the CLBsappear, to facilitate the efficient implementation of user logic.

FIG. 6 illustrates a block diagram of a computing arrangement that maybe configured to implement a system for determining available wirelesscommunication channels in accordance with one or more embodiments of theinvention. Those skilled in the art will appreciate that variousalternative computing arrangements, including one or more processors anda memory arrangement configured with program code, would be suitable forhosting the processes and data structures and implementing the functionsof the different embodiments of the present invention. The computercode, comprising the processes of one or more embodiments of the presentinvention encoded in a processor executable format, may be stored andprovided via a variety of computer-readable storage media or deliverychannels such as magnetic or optical disks or tapes, electronic storagedevices, or as application services over a network.

Processor computing arrangement 600 includes one or more processors 602,a clock signal generator 604, a memory unit 606, a storage unit 608, aninput/output control unit 610, and signal processing hardware 620coupled to host bus 612. The arrangement 600 may be implemented withseparate components on a circuit board or may be implemented internallywithin an integrated circuit. When implemented internally within anintegrated circuit, the processor computing arrangement is otherwiseknown as a microcontroller.

The architecture of the computing arrangement depends on implementationrequirements as would be recognized by those skilled in the art. Theprocessor 602 may be one or more general purpose processors, or acombination of one or more general purpose processors and suitableco-processors, or one or more specialized processors (e.g., RISC, CISC,pipelined, etc.).

The memory arrangement 606 typically includes multiple levels of cachememory and a main memory. The storage arrangement 608 may include localand/or remote persistent storage such as provided by magnetic disks (notshown), flash, EPROM, or other non-volatile data storage. The storageunit may be read or read/write capable. Further, the memory 606 andstorage 608 may be combined in a single arrangement.

The processor arrangement 602 executes the software in storage 608and/or memory 606 arrangements, reads data from and stores data to thestorage 608 and/or memory 606 arrangements, and communicates withexternal devices through the input/output control arrangement 610. Thesefunctions are synchronized by the clock signal generator 604. Theresource of the computing arrangement may be managed by either anoperating system (not shown), or a hardware control unit (not shown).

Receiver 640 is configured to receive radio frequency signals 642 andseparate and output I and Q signal components 644. Signal processinghardware 620, is configured to perform signal processing on I and Qsignal components 644 received from receiver circuit 640. The exampleembodiment shows receiver circuit output coupled to an input of signalprocessing hardware 620. It is understood that receiver circuit 640 mayalternately coupled to host bus 612 and output signal components tosignal processing hardware 620 over the host bus. The signal processingshown in this example embodiment includes a unit for computing theperform Fast Fourier Transform of the received signal 630.

It is understood that other signal processing functions performed by oneor more embodiments of the present invention such as: determining squaremagnitude, determining averages in the time domain, normalization, ordetermining spectral moving averages, may be performed by the processingunit and memory or may alternately be implemented within signalprocessing hardware 620.

FIG. 7 illustrates a block diagram of an example implementation of thesignal processing hardware of FIG. 6 configured to implement severalsignal processing functions. Signal processing hardware 720 includes abus interface 724, input memory 726, output memory 728, and processingblock 730. Input and output memory blocks are included, as shown, may beincluded to improve streaming performance of the signal processinghardware. In this example embodiment, input memory block 726 receivesunprocessed signals from a receiver circuit (not shown) over a data-busvia bus interface 724. One or more embodiments of the invention couplethe output of a receiver circuit to input memory block 726, as shown inFIG. 6.

Processing block 730 receives and processes unprocessed signal input ofa channel. In this example implementation, the processing block includesa block for performing Fast Fourier Transform 732, a block for computingthe square magnitude 734, and a block for computing a time domainaverage 736. It is understood, that other processing blocks forperforming other signal processing functions performed in accordancewith one or more embodiments of the invention may also be included inthe processing block 730.

Those skilled in the art will appreciate that various alternativecomputing arrangements, including one or more processors and a memoryarrangement configured with program code, would be suitable for hostingthe processes and data structures of the different embodiments of thepresent invention.

One or more embodiment of the present invention is thought to beapplicable to a variety of systems for determining available wirelesschannels. Other aspects and embodiments of the present invention will beapparent to those skilled in the art from consideration of thespecification and practice of the invention disclosed herein. It isintended that the specification and illustrated embodiments beconsidered as examples only, with a true scope and spirit of theinvention being indicated by the following claims.

1. A method of determining available wireless communication channels,comprising: determining unreserved frequency bands in a location;selecting a first channel within one of the determined unreservedfrequency bands; monitoring signals received on the first channel for atime duration; estimating a power spectral density of the signals duringthe time duration; determining a spectral moving average of theestimated power spectral density; determining a detection threshold forthe first channel; normalizing the spectral moving average of theestimated power spectral density; determining a percentage of abandwidth of the spectral moving average of the estimated power spectraldensity that exceeds the detection threshold; in response to thedetermined percentage being less than a selected percentage, storingdata indicating the first channel is available; and in response to thedetermined percentage being greater than or equal to the selectedpercentage: determining whether the normalized spectral moving averageof the estimated power spectral density is consistent with a selectedsignal shape; and in response to determining the estimated averagedpower spectral density is not consistent with the selected signal shape,storing data indicating the first channel is available.
 2. The method ofclaim 1, wherein the determining whether the spectral moving average ofthe estimated power spectral density is consistent with the selectedsignal shape includes: determining a peak and slopes of the spectralmoving average of the estimated power spectral density; and wherein thespectral moving average of the estimated power spectral density isconsistent with the selected signal shape if the slopes are within aselected range.
 3. The method of claim 1, wherein the determining of theunreserved frequency bands includes: receiving data in a broadcastcontrol channel indicating an identity of a frequency band reservee; anddownloading data from a database indicating frequency bands reserved forthe reservee.
 4. The method of claim 1, wherein downloaded data includesdata indicating a bandwidth and respective center frequencies of thefrequency bands reserved for the reservee.
 5. The method of claim 1,wherein the determining of the frequency bands reserved for the reserveeincludes downloading data from a database indicating channels reservedat the location.
 6. The method of claim 1, wherein the storing of dataindicating the first channel is available, includes storing dataindicating a level of noise present on the first channel.
 7. The methodof claim 1, further comprising normalizing the spectral moving averageof the estimated power spectral density.
 8. The method of claim 7,wherein normalizing is performed in response to the determinedpercentage being greater than or equal to the selected percentage. 9.The method of claim 1, wherein the estimating of the power spectraldensity includes: determining square magnitudes of an instantaneous FastFourier Transform of the signals; and averaging the determined squaremagnitudes over the time duration.
 10. The method of claim 1, furthercomprising: wherein the determining whether the spectral moving averageof the estimated power spectral density is consistent with the selectedsignal shape includes: determining a peak and slopes of the spectralmoving average of the estimated power spectral density; and wherein thespectral moving average of the estimated power spectral density isconsistent with the selected signal shape if the slopes are within aselected range; selecting a second channel within one of the determinedunreserved frequency bands in response to the slopes being outside ofthe selected range; and repeating the steps of monitoring, estimating,determining transmission threshold and percentage, determiningconsistency with the selected signal shape, and storing using the secondchannel as the first channel.
 11. The method of claim 1, furthercomprising: selecting one or more additional channels within thedetermined unreserved frequency bands; for each of the one or moreadditional channels, repeating the steps of monitoring, estimating,determining detection threshold and percentage, determining consistencywith the selected signal shape, and storing using the respective channelas the first channel; determining a set of available channels from theone or more additional channels and the first channel; and determining achannel in the set of available channels with the lowest power spectraldensity.
 12. A system for determining available wireless communicationchannels, comprising: means for receiving signals transmitted on aplurality of communication channels and output signals received on aselected channel; a data bus coupled to the means for receiving; means,coupled to the data bus, for determining unreserved frequency bands in alocation; means for selecting the selected channel from one of thedetermined unreserved frequency bands and configuring the means forreceiving signals to output signals received on the selected channel;means for determining a power spectral density of the signals output bythe receiver unit; and means for determining from the power spectraldensity whether the signals received on the selected channel areconsistent with a selected signal shape and strength indicating thechannel is not available.
 13. The system of claim 12, further comprisingmeans for applying a spectral moving average window to the powerspectral density.
 14. The system of claim 12, wherein the means fordetermining the power spectral density includes: means for computingFast Fourier Transforms; means for computing the square magnitudescoupled to an output of the means for computing Fast Fourier Transforms;and means for averaging over a time interval coupled to an output ofmeans for computing the square magnitudes.
 15. The system of claim 14,wherein the means for determining the power spectral density furtherincludes means for computing moving averages coupled to an output of themeans for averaging over a time interval.
 16. The system of claim 12,further comprising means for determining a percentage of channelbandwidth used for signal transmission.
 17. The system of claim 12,further comprising: means for determining a spectral moving average ofthe power spectral density; means for normalizing the spectral movingaverage; means for determining peak and average slopes of the normalizedspectral moving average; and means for determining whether the averageslopes are within a selected range of slopes.
 18. The system of claim12, further comprising means for determining unreserved frequency bands,by retrieving data from a database.
 19. A circuit for determiningavailable wireless communication channels, comprising: a receivercircuit configured to receive a plurality of transmitted signals; asignal processing circuit coupled to an output of the receiver circuit;a channel analysis circuit coupled to the signal processing circuit; anda channel selection controller circuit coupled to the channel analysiscircuit and to the receiver circuit; and wherein: the channel selectioncontroller circuit is configured to: monitor the plurality oftransmitted signals received by the receiver circuit; determineunreserved frequency bands in a location; select a first channel withinthe determined unreserved frequency bands; and configure the receivercircuit to output signals received on the first channel; the signalprocessing circuit is configured to determine and output a powerspectral density of signals output by the receiver circuit; and thechannel analysis circuit is configured to: determine a spectral movingaverage of the power spectral density output by the signal processingcircuit; determine a signal detection threshold level; determine thepercent of bandwidth of the first channel with the power spectraldensity above the signal detection threshold level; normalize thedetermined spectral moving average; determine a peak and a slope of thenormalized spectral moving average; and determine from the determinedpercentage of bandwidth and the peak and the slope whether the firstchannel is available.
 20. The circuit of claim 19, wherein in responseto determining whether the selected channel is available: the channelselection controller circuit is configured to: select a second channelfrom the determined unreserved frequency bands; and configure thereceiver circuit to output signals received on the second channel; thesignal processing circuit is configured to determine and output thepower spectral density of signals output by the receiver circuit; andthe channel analysis circuit is configured to: determine a spectralmoving average of the power spectral density output by the signalprocessing circuit; determine a signal detection threshold level;determine the percent of bandwidth of the selected channel with a powerspectral density above the signal detection threshold level; normalizethe determined spectral moving average; determine the peak and the slopeof the normalized spectral moving average; and determine from thedetermined percentage of bandwidth and the peak and the slope whetherthe second channel is available.